1229 band seems to be split, with maxima at 282 nm ([e] -85,900) and 249 nm ([e] +33,100). The lower wavelength band, which the uv spectrum suggests might arise from homoconjugation, is also strongly split with C D peaks at 236 nm ([e] -220,000) and 221 nm ([e] +53,300). This indicates that these two indene transitions are capable of a preferred long-axis B-mode coupling (levo in the S enantiomer) and an energetically less favored A-mode. The high rotatory power shown in these C D peaks indicates that homoconjugation as
shown in Figure 14 may augment this coupling. If so, this system exhibits simultaneously the characteristics of a coupled oscillator and a twisted composite chromophore. We conclude that studies of the chiroptical properties of suitable sets of “monomeric” and “dimeric” chromophoric systems can, indeed, provide detailed insights into the ways in which these chromophores respond to light2-insights available at present in no other way.
Dissymmetric Spirans. 11.’ Absolute Configuration of 1,l ’-Spirobiindene and Related Compounds2 Richard K. Hill* and David A. Cullison3 Contribution from the Department of Chemistry, University of Georgia, Athens, Georgia 30601. Received June 20, 1972 Abstract: The optically active spirans, 1,l ‘-spirobiindan, 1,l ‘-spirobiindene, and 1,l ‘-spirobiindan-3-one, have been prepared from optically active 3-carboxymethyl-3-phenyl-1-indanone, an intermediate possessing centrodissymmetry. Correlation of its configuration with two independent standards of absolute configuration, 2-methyl-2-phenylsuccinicacid and 1-cyclohexyl-1-phenylethanol, allowed unambiguous assignment of absolute configuration to the series of spiroindans. The spectroscopic properties of the spiro compounds, which show evidence of spiroconjugation, are discussed.
T
he determination of absolute configuration of molecules possessing axial symmetry, Le., those which are dissymmetric but not a ~ y m m e t r i ccontinues ,~ to pose intriguing problems because of the absence of a formal asymmetric carbon which might serve as the basis for configurational correlations. Molecules of Cz symmetry, such as allenes, spirans, hindered biphenyls, hexahelicene, and trans-cyclooctene, are of particular interest, and ingenious solutions have been provided for these cases by both chemical5 and crystallographica methods. Because of their relatively rigid geometry, spirans offer the opportunity to study interactions between functional groups held in fixed relative orientations, and consequently are useful substrates for chiroptical studies. Unambiguous assignments of absolute configuration to chiral Cz spirans were not made until 1968-1969, when configurations were established for spirans l’, 2,’ and 3.8 More recently, assignments (1) For the first paper in this series, see G. Krow and R. K. Hill,
Chem. Commun., 430 (1968). (2) Grateful acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. (3) NDEA Fellow, 1969-1972. (4) K. Mislow, “Introduction to Stereochemistry,” W. A. Benjamin, New York, N. Y., 1965, p 25. ( 5 ) G. Krow, Top. Stereochem., 5 , 31 (1970). (63 D. A. Lightner, D. T. Hefelfinger, T. W. Powers, G . W. Frank, and K. N. Trueblood, J. Amer. Chem. SOC.,94, 3492 (1972); H. Akimoto, T. Shioiri, Y. Iitaka, and S. Yamada, Tetrahedron L e f t . , 97 (1968); P. C. Manor, D. P. Shoemaker, and A. S . Parkes, J . Amer. Chem. Soc., 92, 5260 (1970); L . A. Hulshof, A. Vos, and H. Wynberg, J . Org. Chem., 37, 1767 (1972).
(7) (a) H. Gerlach, Helu. Chim. Acta, 51, 1587 (1968); (b) D. A. Lightner, G. D. Christiansen, and J. L. Melquist, Terrahedron Lett., 2045 (1972). (8) J. H. Brewster and R. S . Jones, Jr., J. Org. Chem., 34, 354 (1969).
of absolute configuration have been made to spirans 4,9 5,lo and 6,’’ using empirical rules or deductions from chiroptical properties. In compounds 1, 3, and4 the spiro atom is bonded to four methylene groups; not surprisingly there is no evidence of electronic interaction between the two rings and the optical rotations are generally modest. Only in 2 and 5 was it possible to relate rotatory dispersion to absolute c o n f i g ~ r a t i o n . ~ Consequently ~~’~ it appeared worthwhile to investigate spiran systems in which aromatic rings and other unsaturated chromophores were linked directly to the spiro carbon, leading to enhancement of rotatory strengths and possibly detection of spiroc o n j u g a t i ~ n ~in~ ~ ORD ’ ~ as well as uv spectra. We undertook the preparation, resolution, and determination of absolute configuration of 1,l ’-spirobiindene (7). While this work was in progress Professor J. H. Brewster informed us of similar studies on 7 and its derivatives in his 1ab0ratory.l~ Very recently an extensive series of optically active tetramethyl-I, 1 ’spirobiindans of structure 8 as well as the spirobiindanol 9 has been reported, and absolute configurations were assigned both by theoretical calculations of O R D spectra and by X-ray analysis. (9) H. Wynberg and J. P. M. Houbiers, ibid., 36, 834 (1971). (10) G. Haas, P. B. Hulbert, W. Klyne, V. Prelog, and G . Snatzke, Helu. Chim. Acta, 54, 491 (1971). (11) H. Falk, W. Frostl, and K . Schlogl, Monatsh. Chem., 102, 1270 11971). -,\ - -
(12) H. E. Simmons and T. Fukunaga, J . Amer. Chem. S O ~ .89, , 5208 (1967). (13) R. Hoffmann, A. Imamura, and G. D. Zeiss, ibid., 89, 5215
(1967).
(14) J. H. Brewster and R. T, Prudence, ibid.,95, 1217 (1973). We thank Professor Brewster for communicating his results to us and suggesting concurrent publication.
Hill, Cullison
1,I ‘4pirobiindene
1230 Chart I. Preparation of 1,l'-Spirobiindans
J
0
T 5
4
6
13
7
14
8
A
15, X = OH 16, X = Br
9
Synthesis and Resolution. In order to provide an intermediate possessing both a functional group which would allow easy resolution and an asymmetrically substituted carbon atom which might later permit straightforward configurational correlations with standards of known configuration, the synthesis of 7 was designed around 3-carboxymethyl-3-phenyl-] -indanone (12). Though the synthesis of acid 12 has already been reported,'* we found that it could be prepared more simply and in higher yield than the previous method by intramolecular Friedel-Crafts cyclization of 3,3-diphenylglutaric anhydride (11). Further ring closure to the spirobiindanone 13 was effected in good yield by heating with polyphosphoric acid. The same conditions were effective in forming the diketone directly from 3,3-diphenylglutaric acid (lo), making the racemic diketone easily available in quantity. Wolff-Kishner reduction of 13 led smoothly to 1,l'spirobiindan (14). l9 This hydrocarbon could also be prepared by hot acid cyclization of 1,5-diphenyl-3pentanone, itself readily available by hydrogenation of dibenzalacetone. This latter simple route makes racemic 14 easily accessible, though of course it is not amenable to preparation of optically active compounds. For preparation of the corresponding 1,l '-spirobiindene (7), 13 was reduced with sodium borohydride to a stereoisomeric mixture of diols 15, dehydrated by (15) S . Hagishita, I
